You will never - with normal analog TV signals - get to that.
There are simply not 800 columns displayed on any TV standard, by most sensible measures.

For example - NTSC - yes - it has around 480 displayable rows, but the maximum luminance frequency is 4.5MHz - which divided by the line rate is 285.

http://www.maxim-ic.com/app-notes/index.mvp/id/734 - the active picture is 52/64ths of the line, so 52/64 * 285 = 231 complete cycles.

This means the image can go from black to white 231 times, or you might call this 462 pixels.

In practice, no normal reciever will quite do this, as the sound would begin to bleed through as high frequency artifacts, the real limit will be somewhat lower - perhaps around 420 pixels.

The colour bandwidth is considerably lower - if you want to display a red/green crosshatch, then this is around a resolution of 150 pixels.

The horizontal numbers for PAL are similar.